Getter for x-ray generators



May 13, 194-1. z J ATLEE 2,242,100

GETTER FOR X-RAY GENERATORS Filed May 26, 1939 INVENT OR.

Zea l ffllee' W ATTORNEY-5 Patented May 13, 1941 GETTER FOR X-RAYGENERATORS Zed J. Atlee, Elmhurst, 111., assignor to General ElectricX-Ray Corporation, Chicago, 111., a cor poration of New York ApplicationMay 26, 1939, Serial No. 275,877

4 Claims. (Cl.

My invention relates in general to X-ray generators, and has moreparticular reference to the provision of means to facilitate theconditionin of the generator for operation after the same has beenfabricated.

An important object of the present invention K is to provide gettermeans in an X-ray generator for conditioning the same for operation.

Another important object is to provide an X- ray generator comprisingcooperating anode and cathode means enclosed in a sealed envelope, thegetter being disposed in the envelope in a pocket formed therein remotefrom the active portions of the anode and cathode means, whereby theactuation of the getter may not impair or'contaminate the anode andcathode means.

Another important object is to form and arrange the getter so that theforces generated in flashing the same will be directed into an encathodemeans.

Another important object is to provide getter means for X-ray generatorscomprising a material holder of improved form to direct the flash anodeand cathode elements; a further object being to provide a mounting forsupporting the getter holder on one of the active elements of the X-raygenerator, the holder being formed from'the anode and cathode means, asin a pocket formed in the envelope of the X-ray generator.

Another important object resides in using a getter materialcharacterized by a reluctance the material preferably comprising bariumand/or aluminum or other suitable non-migratory material having a highmelting point, where by the end products of the flash may be localizedinnocuously in the remote envelope pocket in which the getter means ispreferably mounted.

The foregoing and numerous other important objects, advantages andinherent functions of the invention will become apparent as the same isvelope pocket and away from the'anode and 1 products away from theactive portions of the to support the holder element in position remoteto migrate in the envelope upon flashing therein, T

more fully understood from the following descrip- 5 along line 2-2 inFigure 1, showing the details of the getter means illustrated in Figurel;

' Figure 3 is a sectional View taken longitudinally through the end ofan X-ray generator to illustrate a modified form of getter means and themanner of mounting the same in accordance with the present invention;and

Figures 4 and 5 are sectional views taken substantially along the lines4-4 in Figure 3 and lines 5-5 in Figures 2 and 4, respectively.

To illustrate my invention, I have shown on the drawing an X-raygenerator comprising a cathode II and an anode in spaced-apartrelationship and in position to cooperate to cause the anode to functionas a source of X-rays when energized by electronic action set up by theoperation of the cathode. The anode and cathode are enclosed in apreferably glass envelope l5, being sealed in the envelope at theopposite ends thereof. The envelope, as shown on the drawing, comprisesa central enlarged portion l 9 formed at its opposite ends withsleeve-like extensions 2!. The outer ends of the extensions may beturned inwardly to form reentrant sleeve portions 23 on said envelope,and the active elements of the X-ray generator may be mounted on saidreentrant sleeve portion and sealed thereon, as at H. Although in Figure1 I have shown only the cathode seal, it will be understood that theanode likewise may be sealed in the opposite end of the envelope in likeor other suitable or preferred fashion.

The cathode H is preferably provided with a dependent skirt portion 25extending therefrom within the envelope extension 2| to enclose and forma shield for the seal I! in order to prevent impingement on said seal ofstray electrons liberated within the envelope, thereby preventing theseal from becoming deteriorated through electron impact.

It will be noted that the envelope extension 2| and the reentrant sleeveportion 23 form therebetween an annular space 21 into which theterminaledges of the skirt portion 25 extend. The envelope walls also may beoffset, as at 29, so that the terminal portions of said annular space 21are of restricted character forming a pocket 3|.-

After the parts II and I3 have been assembled within the envelope 15,the device is evacuated by connecting the envelope with exhaust means,such as a molecular pump, the connection being made as at 33.

In conditioning the generator for operation, it is necessary to removenot only all of the gas that is present within the envelope, but alsothe occluded gas contained in the anode and cathode and in the materialof the envelope itself. If such occluded gases are not removed, theywill gradually be released Within the envelope and impair the exhaustedcondition at which the generator is designed to operate.

The removal of the occluded gases is accomplished by baking or otherwiseheat treating the entire device at a temperature short of the softeningpoint of the glass, while keeping the exhaust means in operation, andalso by heating the electrodes to a high temperature, either by electronbombardment or by placing the electrodes in a magnetic field fluctuatingat frequencies of the order of radio frequency.

After all of the occluded gases and other impurities have thus beenremoved from the envelope, the exhaust connection may be sealed off, asat 34. I propose, as a final step, to volatilize or flash a smallquantity of a suitable getter 35 within the envelope after the envelopehas been sealed, in order to form end products of the getter materialand any remaining gases, the end products being innocuous and remainingin the envelope.

As a getter material, I prefer to employ a metal, such as ban'um and/oraluminum, and preferably a mixture of the named metals, the gettermaterial having a high melting point and being characterized by atendency to remain immobile in the envelope after being flashed.

The getter material 35 is preferably used in finely-divided or powderedform and is supported in a holder 31 which in turn is mounted on asupport 39 anchored on one of the active elements of the X-ray generatorand preferably on the skirt 25 in position such that the holder 3'! isdisposed in the restricted pocket 3| in a position as far removed fromthe active portions of the anode and cathode as is possible.

The support '39 preferably comprises a sheet metal strip suitablysecured, as at 5|, on the skirt and having an offset portion 53terminating in a curled mounting forming a seat to which the holder 31may be secured.

The support 39 and the holder 31 are so formed, arranged and mountedthat the flange 49 substantially closes and forms a barrier between thespace 3| and the remaining portions of the envelope in which the activeelements H and l3 of the generator are disposed. The holder 3i,moreover, is disposed in the chamber 3| in position such that the flashproducts will impinge directly upon the facing surface of the envelopeportions which define the side of the chamber 3| where said flashproducts will adhere as a film indicated in dotted lines at 59. Theenvelope surfaces defining the pocket 3|, being at the end of theenvelope, comprise a cool region on which flash products will readilycondense to form the film 59.

The operation of the getter may be accomplished in any suitable orconvenient fashion,

as by heating the .getter by inductive action to a temperature above theflash point of the getter material. After flashing, the flash productswill remain in filmed form, as at 59, in substantially immobilecondition and ordinarily will not migrate nor deleteriously aifect theoperation of the elements I and I3.

The getter material 35 is preferably arranged within a tubular wire SIof electrical conducting material, one side of which wire is of reducedsection, as at 53. This wire may then be supported in any suitable orconvenient fashion on the support 39, in position such that the portionof reduced section 63 faces into the pocket 3|. The getter may beflashed by heating the same in its enclosing sheath 6| inductively,whereupon the flash products will be expelled outwardly through the Wallof reduced section 63, to form the deposit 58 on the facingpocketforming walls of the envelope.

Preferably, however, the getter is flashed by providing for the heatingof the same by passage of an electrical current through the sheath orcontainer GI, and this may be accomplished by anchoring the member 6| atone end on the support 39, and by providing conductor means 65electrically connecting the other end of the member 6| with a source ofgetter flashing electrical power outwardly of the envelope IS, theconductor means 65 being electrically connected witha seal conductor 61extending outwardly of the envelope through the seal 69. This seal 69also contains a ground conductor for electrically connecting the body ofthe electrode I including the skirt portion 25, outwardly of theenvelope; and by utilizing this ground conductor and the conductor 61,electrical current for flashing the getter may be delivered within theenvelope from a suitable external power source.

In certain electrode constructions the getter" flashing conductor 61 maycomprise one of the cathode conductors, and in such constructions it isnot necessary to provide an additional seal conductor for the solepurpose of flashing the getter, but the cathode lead may be used forthat purpose.

As shown in Figures 1 and 2, the member 6| may be supported on a guard13 similar to the guard 3'! and having a flange 19 adapted to serve as aguard and prevent the flash products of the getter material from passingout of the pocket 3|, the support member 13 having a plate portion 1|upon Which the member 6| is mounted, the member 6| being electricallyconnected at one end on the plate H and arranged in a spiral coil, asshown.

Means may be provided, if necessary, to support the several coils andinsulate the same from the plate H, as by means of glass beads orpredestals formed on the plate 1| to support the member 6| in place, thefree end of the member 6| being connected with the conductor 65.

As shown in Figures 3 and 4, the member 6| is arranged as asubstantially annular loop in the annular pocket 3|, with the wallportion 83 facing the bottom of the annular pocket, one end of the loopbeing supported on the member 39 and the other being connected with theconductor means 65. When mounted in such fashion, it is not essential toprovide a guard similar to the flange 49 and 79. However, an annularplate 89 forming a guard may be provided, desired, and anchored on themember 39 to extend in the pocket 3|, and the member 6| containing thegetter material may be supported on the annular guard 89 in positionbetween said guard and the bottom of the pocket 3|.

The member 6| in such case may be electrically connected at one end onthe guard 89 and thus grounded on the electrode body, and the other endof the member 6| may be electrically connected, as shown, with the flashconductor 65. The intermediate portions of the member 6| may bemechanically secured on and insulated from the guard 89 as by means ofglass mountings or other suitable supporting and insulating means on theguard 89.

Flashing of the getter, however, substantially reduces the amount ofoccluded gas remaining in the envelope and permits the provision of anX-ray generator in which, occluded gases will not be liberated duringthe operation of the tube. Consequently, tubes flashed in accordancewith my present invention will operate satisfactorily for extendedperiods without becoming soft.

It is thought that the invention and numerous of its attendantadvantages will be understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the form herein described being a preferred embodiment for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. An X-ray generator comprising co -operating electrodes enclosed in anenvelope, means on said envelope forming a pocket having a wallproviding a cool zone at an end of the envelope, getter means comprisinga tubular sheath form ing a holder for getter material, said sheathhaving a wall of reduced sectional thickness along a side thereof andbeing arranged in a spiral pancake coil, and means for supporting saidsheath in said pocket with the wall portions of reduced section facingthe pocket-forming wall.

2. An X-ray generator comprising co-operating electrodes enclosed in anenvelope, means on said envelope forming an annular pocket having a wallproviding a cool zone at an end of the envelope, getter means comprisinga tubular sheath forming a holder for getter material, said sheathhaving a wall of reduced sectional thickness along a side thereof andbeing arranged as a loop extending in the annular pocket, and means forsupporting said sheath in said pocket with the wall portions of reducedsection facing the bottom of the pocket.

3. An X-ray generator comprising co-operating electrodes enclosed in anenvelope, means on said envelope forming a pocket having a wallproviding a cool zone at an end of the envelope, getter means comprisinga tubular sheath forming a holder for getter material, said sheathhaving a wall of reduced sectional thickness along a side thereof, meansto support said sheath on one of said electrodes, and a guard arrangedin the pocket between the sheath and the electrode on which the sheathis mounted.

4. An X-ray generator comprising co-operating electrodes enclosed in anenvelope, means on said envelope forming a pocket having a wallproviding a cool zone at an end of the envelope, getter means comprisinga tubular sheath forming a holder for getter material, said sheathhaving a wall of reduced sectional thickness along a side thereof, asupport electrically connected with one of said electrodes, means toelectrically connect a portion of said sheath on said support and toinsulate the remaining portions of said sheath from said support, andmeans sealed in said envelope for electrically connecting a portion ofsaid sheath remote from said support connected portion with a source ofgetter flashing power outwardly of said envelope.

ZED J. A'I'LEE.

